Harnessing tunable lignin-based carbon quantum dots for sustainable water purification

Developing on-demand biomass valorization represents an ideal path to alleviate the double burden of sustainable energy-environment future, yet exploring tunable lignin-first chemistry to accomplish multifunctional water purification remains elusive. Herein, we report a versatile solvent-fractionation to construct heteroatom-doped multicolor lignin carbon quantum dots (CQDs) with the functions of bimodule pollutant sensing, metaL-ionic visualization, and photocatalytic antibiotic dissociation. With the aid of oxidation cleavage and biphasic extraction, the underlying lignin features of molecular weight and functional linkages influence the quantum size and core-surface state of CQDs conferring the unique opticaL-structure-performance. The N, S co-doped blue-emitting CQDs via light-quenching offers the selective identification of Fe³⁺-ions in a broad response range with acceptable limit of detection. The addition of L-cysteine can efficiently restore the fluorescence of CQDs by forming a stable Fe³⁺-L-cys complex. The green-emissive CQDs is facilely embedded into cellulose hydrogel to directly visualize the presence of metaL-ions. A red-CQDs modified ternary ZnIn₂S₄ (ZIS) composite is fabricated to achieve photocatalytic antibiotic removal with an efficiency of ~85%. The excellent photo-generated electron and storage capabilities of CQDs improve the light-capturing, electron conduction, and charge carriers separation of ZIS. The reactive species are of importance to photocatalytic tetracycline oxidation, wherein the electron holes (h⁺) function as the main contributor followed by ·O₂^-, ¹O₂ and ·OH. The directly interfacial electron escaping-shuttling with the help of optimized electronic and energy-band structures is confirmed via electrochemical test and theoretical computation. We anticipate that the present work not only sheds a substantial light to manipulate polychromatic lignin-based CQDs via a tailored solvent-engineering, but also presents an emerging green route of emphasizing biomass-water nexus.